Najib Bouaanani

Seismic Performance of Circular High-Strength Concrete Columns

Little experimental research is available for high-strength columns (HSC) under combined cyclic flexure and axial loads. This paper seeks to fill this gap by presenting results from tests of six large-scale spirally reinforced HSC circular columns under reverse cyclic flexure and constant axial loads. The tests were conducted to examine the post-elastic behavior and the ductility level reached by HSC circular columns designed according to the 2004 Canadian Standards Association A23.3 requirements for transverse steel reinforcement. The columns were subjected to constant axial loads and a cyclic horizontal load-inducing reversed bending moment. Findings show that columns designed according to the confinement reinforcement requirements of the Canadian standard can achieve adequate ductility if the transverse reinforcement chosen accounts for the axial load level and the transverse-steel yield strength. Concrete columns that have different transverse-steel yield strength and different axial-load levels will have adequate sectional ductility.

Experimental and Numerical Assessment of the Three-Dimensional Modal Dynamic Response of Bridge Pile Foundations Submerged in Water

This paper describes an experimental program conducted to investigate the effects of fluid-structure interaction on the modal dynamic response of three reduced-scale bridge pile foundations submerged partially or totally in water. The vibration periods of the specimens are measured for the two lateral modes and first torsional mode using ambient and forced vibration tests. The results are presented and discussed as a function of surrounding water levels and the number and geometrical patterns of the piles. Three-dimensional (3D) finite-element models of the tested specimens surrounded by different water levels are built, and the results are successfully validated against the obtained experimental data. The built numerical models are used to compute 3D modal hydrodynamic pressures. A systematic analysis of the period ratios and 3D hydrodynamic loads is presented to characterize the effects of pile cap, water height, and the number and geometrical pattern of the piles on dynamic response. The experimental and numerical results of this research allow a better understanding of the complex dynamically induced fluid-structure interaction effects in the response of deepwater bridge pile foundations.

Finite Difference Thermoelastic Analysis of Suspended Cables Including Extensibility and Large Sag Effects

This paper presents and validates an original and practical finite difference model to investigate the thermoelastic response of suspended cables. The mathematical formulations are provided for various loading cases. The model includes the effects of cable extensibility and large sag, as well as variability of temperature gradients and thermal properties of the cable along its arc-length. The formulations are programmed and used to study suspended cables subjected to different thermomechanical loads. The results are validated against analytical or finite element solutions, and the proposed model is shown accurate and efficient in assessing the thermoelastic response of suspended cables.

A novel scheme for large deflection analysis of suspended cables made of linear or nonlinear elastic materials

This paper presents a new approach to investigate the static response of horizontal and inclined suspended cables with deformable cross-section, made of general linear or nonlinear elastic materials, and subjected to vertical concentrated and distributed loads. The proposed technique also includes large sag and extensibility effects, and is based on an original finite difference scheme combined to a nonlinear least squares numerical solution. The mathematical formulation is developed for various loading cases, and an innovative computational strategy is used to transform the resulting nonlinear system of equations into a scaled nonlinear least squares problem. The numerical scheme is programmed and its application illustrated through examples highlighting the effects of coupling between the tension in a cable and the deformation of its cross-section as well as the use of cables made of neo-Hookean materials. The results obtained are in excellent agreement with analytical solutions when available. The proposed technique can be easily programmed and constitutes a valuable tool for large deflection analysis of suspended cables made of nonlinear elastic materials.

Real-Time Dynamic Substructuring Testing of a Bridge Equipped with Friction-Based Seismic Isolators

This paper presents a real-time dynamic substructuring (RTDS) test program that was carried out on a bridge structure equipped with seismic isolators with self-centering and friction energy dissipation capabilities. The structure studied also included bearing units with sliding interfaces providing additional energy dissipation capacity. In the RTDS tests, the seismic isolator was physically tested in the laboratory by using a high performance dynamic structural actuator imposing, in real time, the displacement time-histories obtained from numerical simulations that were run in parallel. The integration scheme used in the test program was the Rosenbrock-W variant and the integration was performed by using the MathWorks’s Simulink and an XPC target computer environment. The numerical counterpart included the bridge piers and the additional energy dissipation properties. The nonlinear response of these components was accounted for in the numerical models. The RTDS tests were performed in the direction parallel to the length of the bridge. The effects of various ground motions and the influence of modeling assumptions such as friction and column stiffness were investigated. Finally, the test results were compared to the predictions from dynamic time-history analyses performed by using commercially available computer programs. The results indicate that simple numerical modeling techniques can lead to an accurate prediction of the displacement response of the bridge seismic protective systems studied.

Practical Formulas for Frequency Domain Analysis of Earthquake-Induced Dam-Reservoir Interaction

Dam-reservoir dynamic interactions are complex phenomena requiring advanced mathematical and numerical modeling. Although available sophisticated techniques can handle many aspects of these phenomena, simplified procedures are useful and still needed to globally evaluate the dynamic response of dam-reservoir systems. This paper presents and validates an original practical procedure to investigate earthquake induced dam-reservoir interaction in the frequency domain, including the effects of dam flexibility, water compressibility, and reservoir bottom wave absorption. The procedure relates hydrodynamic pressure due to any deflected modal response of a two-dimensional gravity dam on a rigid foundation to hydrodynamic pressure caused by a horizontal rigid body motion. New analytical expressions that can be easily programmed in a spreadsheet package or implemented in a dam structural analysis program are also proposed to conduct simplified fundamental mode earthquake analysis of gravity dams. The techniques presented can be efficiently used to provide valuable insight into the effects and relative importance of the various parameters involved in the dynamic response of dam-reservoir systems. Although the mathematical derivations and closed-form expressions developed were applied to dam-reservoir systems herein, they can be easily adapted to other fluid-structure interaction problems.

On computation of conditional mean spectrum in Eastern Canada

This paper investigates the main ingredients required to compute Conditional Mean Spectra (CMS) in Eastern Canada and assesses their effects on the obtained CMS. We particularly address the influence of ground motion prediction equations (GMPEs) and correlations between spectral accelerations. CMS are computed using two approximate methods, and the results are illustrated for three locations with different seismic hazard and risk levels. It is found that selection of GMPEs considerably influences the CMS, particularly at shorter periods. A database of historical records from Eastern Canada is studied to obtain correlation coefficients. The results suggest higher spectral correlations than predicted by a model based on ground motions from Western North America (WNA). The sensitivity of correlation coefficients to magnitude and epicentral distance is also verified, revealing that magnitude has a more significant effect on these coefficients than distance. We also show that the effect of magnitude- or distance-based correlation coefficients on the CMS is (1) generally negligible at long periods and (2) significant at shorter periods particularly when the conditioning period is less than approximately 0.5 s. This work is the first study addressing in detail the ingredients and construction of CMS in Eastern Canada. The methodology and results discussed are expected to enhance the application of CMS in this region.

An improved HSFR method for natural vibration analysis of an immersed cylinder pile with a tip mass

Abstract Immersed cylinder piles are usually modelled as immersed cantilever cylinder columns carrying a tip mass and rotary moment of inertia. In this paper, the equations of motion of an immersed cylinder pile along transversal modes of vibration are developed. Compressibility of water and structural damping are included in the formulation. Natural frequencies of the immersed pile are obtained from the developed equations using harmonic sweep frequency response analyses. The proposed method is applied to numerical examples, and the results obtained are shown satisfactory when compared to other numerical solutions in the literature, or to finite element solutions and experimental data.

Damping Reduction Factors for Crustal, Inslab, and Interface Earthquakes Characterizing Seismic Hazard in Southwestern British Columbia, Canada

High-damping displacement spectra and corresponding damping reduction factors (η) are important ingredients in seismic design and analysis of structures equipped with seismic protection systems, as well as in displacement-based design methodologies. In this study, we investigated η factors for three types of earthquake characterizing seismic hazard in southwestern British Columbia, Canada: shallow crustal, deep inslab, and interface subduction. We used a large and comprehensive database including records from recent relevant earthquakes, such as the 2011 Tohoku event. Our key observations were as follows: (1) there is negligible dependence of η on soil class; (2) there is significant dependence of η on the frequency content and duration of ground motions that characterize the different record types, and (3) η is dependent on period, particularly for inslab events. Period-dependent equations were proposed to predict η for damping ratios between 5% and 30% corresponding to the three event types.

Accounting for Earthquake-Induced Dam-Reservoir Interaction Using Modified Accelerograms

AbstractThis paper proposes a new practical and efficient procedure to investigate the seismic response of gravity dams that (1) avoids the finite or boundary element discretization of the impounded reservoir; (2) can be applied using standard finite-element software not necessarily including fluid-structure interaction capabilities; and (3) accounts for dam and foundation flexibility, water compressibility, and reservoir bottom wave absorption. The proposed technique consists of modifying the original input ground acceleration to obtain a new accelerogram that directly accounts for the complex effects of fluid-structure interaction. This new accelerogram can then be applied to a dam or dam-foundation system without the impounded reservoir. The exact and simplified formulations of the proposed method are developed, and its efficiency is validated through examples of dam-reservoir systems with different geometries. Very satisfactory agreement is obtained when comparing the results to more advanced finite-e...